Question
I have recently had two cases (pediatric cases)where there has been a wave I or Wave I and III but no wave V. That is unless you count the huge wave that is between 8.5 and 11.5 msec. Could this recording possibly be a PAM response? One child was under general anesthesia and the other one was in natural sleep (but she kept waking up and the overall response was made up of some artifact. At what latency is the PAM usually seen? I was under the understanding that if the child was under anesthesia then a PAM was unlikely to be present, is this true? In both of these cases the Wave I and Wave III were very slightly prolonged and in one case there is a good chance there is some brainstem damage. If that large wave is not the PAM, does anyone have any suggestion as to what it could be or why I would have a good Wave I and III, but no V?
Answer
This audiologist asks a couple of questions. I would first suggest to her that the large wave she is seeing at 8.5 and 11.5 ms, is much to early to consider it a PAM response. The normative data suggest this wave is present at 18 to 30 ms. Further I do not see the sedation to be the concern. Without seeing the data, the best I can do is provide suggestions. I have done a good number of sedated ABRs on children in the OR. Invariably I am always playing with filtering and unplugging every thing I can in the OR suite that is nonessential, in attempt to eliminate unwanted interference. The wave as she describes it, suggests to me to be some form of interference. If one monitors the live EEG data, often you can see spikes of interferences with in this data. I will also move my amplifier and adjust the electrode leads, I have even rotated the bed in another direction. If I still have no change I have wrapped my leads in towels or added an additional ground on the patient. In short I will try anything in attempt to rid the unwanted noise. When you work in a busy OR area, you just can not get rid of it all. I finally got our hospital to give me the end suite where I will not have procedures going, on both sides of me. This limits only one procedure to the farthest wall with in the suite I use. I hope I have been of some assistance, OR work with ABR testing can truly be a real challenge at times. While working with children I have now started using the SSABR system and find my results are far better than with standard ABR. I still have some issues with background interference, but not as much.
Dr. Larry G. Martin
Larry G. Martin, AuD, maintains a practice as a medical audiologist at Trinity Health in Minot, North Dakota. He initiated and co-directs the first universal newborn hearing screening program in the state of North Dakota. Dr. Martin is the Technology Coordinator for First Sounds of North Dakota which is a federally funded project designed to place equipment and train personnel in every hospital in North Dakota in order to create a universal newborn hearing screening program throughout the state. Dr Martin is also an adjunct instructor in Audiology at Minot State University.